This invention relates to an oxide superconductor which has a high critical temperature and a high critical current density, and a method for manufacturing such an oxide superconductor.
In prior art, oxide superconductors are known which have a critical temperature in excess of 77K which is the boiling point of nitrogen so that they can be utilized being refrigerated by liquid nitrogen. Examples of such oxide superconductors are Y--Ba--Cu--O, Bi--Sr--Ca--Cu--O and Tl--Ba--Ca--Cu-0. These oxide superconductors are generally obtained by heating starting materials such as oxides and carbonates at about 800.degree.C., thereby thermally decomposing them, carrying out a solid phase reaction, grinding the product, compression molding the ground product and then sintering it.
However, the aforesaid conventional oxide superconductors had the disadvantage that their critical current density fell sharply when they were placed in a magnetic field. In particular, when oxide superconductors were used at liquid nitrogen temperature (77K), there was far more thermal disturbance than when metal superconductors are used at liquid helium temperature (4.2K), as a result of which there was a pronounced flux creep which rendered these oxide superconductors unsuitable for practical application. It has been demonstrated that pinning centers are effective in improving the current density and reducing the effect of flux creep in magnetic field, but no specific method of introducing pinning centers into oxide superconductors had yet been proposed.